Optical pH and carbon dioxide sensors are an active area of research [Leiner, Marc J. P., Wolfbeis, Otto S. In Fiber Optic Chemical Sensors, Wolfbeis, Otto S., Ed., Chapter 8, CRC Press: Boca Raton, 1991]. Recently, several pH sensitive seminaphthorhodaflor dyes have been reported which can be excited in the green part of the spectrum and have emission from both the acid and base tautomers [Whitaker, James E., Haugland, Richard P., Prendergast, Franklyn G. Anal. Biochem., 1991, 194, 330-44]. Fiber optic sensors fabricated with these seminaphthorhodaflor dyes have many advantages over conventional sensors. For example, such sensors may use inexpensive green light emitting diodes and the ratio between the emission from the base peak and the isosbestic point, in contrast to the emission from the base peak alone, is impervious to many effects associated with luminescence-based optic fiber sensors such as bending loss, connector loss, photobleaching, etc. Consequently, fiber optic sensors fabricated with seminaphthorhodaflor dyes inherently have much lower drift than current fluorescent sensors.